1. Field of the Invention
The present invention generally relates to a wind turbine rotor designing method, a wind turbine rotor design support apparatus and a wind turbine rotor, and in particular to a designing technique for avoiding a contact of a wind turbine blade used in a wind turbine generator with a tower and further reducing the pitch moment.
2. Description of the Related Art
One problem accompanied by extension of the diameter of the wind turbine rotor of an upwind type wind turbine generator, that is, large-scaling of the wind turbine blades is increase in the bending amount of the wind turbine blades due to the wind load. A wind turbine blade may contact the tower when the bending amount of the wind turbine blade is increased, and it is therefore necessary that the wind turbine generator is designed so as to avoid contact of wind turbine blades with the tower in consideration of the bending amount of the wind turbine blades.
Three techniques are known for avoiding contact of the wind turbine blades with the tower. A first technique is to previously incline the pitch axes of the wind turbine blades (axes about which the wind turbine blades rotate) toward the windward side (i.e., provision of the cone angle). A second technique is to previously bend the wind turbine blades toward the windward side (i.e., pre-bend). A third technique is to make blade root attachment planes have an inclination angle with respect to the pitch axes so that the wind turbine blades are diagonally attached with respect to the pitch axes (i.e., root cut). In any of these techniques, the tip ends of the wind turbine blades are kept away from the tower and the contact of the wind tower blades with the tower is effectively avoided. Such techniques are disclosed in, for example, U.S. Patent Publication No. 2009/0304513 A1, U.S. Pat. No. 6,582,196 B1, U.S. Patent Publication No. 2010/0104444 A1, and German Patent Application No. 10 2006 041 383 A1.
The mere use of these techniques does not, however, dissolve a problem that the pitch moment required for rotating a wind turbine blade about the pitch axis is increased when the wind turbine blade is large-sized and the imbalance of load exerting on the blade rotation bearing is increased. Rather, in some case, there is even a case that the imbalance of the load exerted on the blade rotation bearing is increased on the contrary. The increase in the pitch moment necessitates increase in the driving ability of the pitch control mechanism which is mounted on the rotor head, and this is not preferable in designing a wind turbine generator. If the pitch moment required for rotating the wind turbine blade about the pitch axis is reduced by the design of the wind turbine blades, however, such a problem would be avoided.
According to a study by the inventors, use of an optimum designing technique allows reducing the pitch moment required for rotating a wind turbine blade about the pitch axis. No reference is found in the known techniques mentioned above as to reduction of the pitch moment.